The invention relates generally to the extrusion and cutting of thermoplastic material, and more particularly to using feedback from a temperature sensor to provide control over the cooling rate of the extruded material to improve the process of cutting the extrusion.
Methods and systems are known in the art for simultaneously producing and cutting a thermoplastic extrusion in a continuous process. For example, the apparatus may include an extruder to produce a continuous extrusion, whether hollow or solid. In association with the extruder, such apparatus may include a vacuum chamber, in the case of hollow extrusions, and a cooling chamber to cool the extrudate as it is extruded. A belt or rollers may also be provided to feed the extrudate from the extruder to a cutting blade which can cut the extrudate to desired lengths The vacuum chamber can help support a hollow extrusion until it is sufficiently cooled to maintain its shape. Where the extrusion is solid or semi-hollow (such as a channel), one or more devices known as calibrators can be used in place of the vacuum chamber in order to align and size the extrusion as it is produced and until sufficiently cooled The calibrators can have internal passageways forming cooling circuits through which coolant can be circulated to cool the extrudate as it passes through the calibrators. Such known apparatus can further include a cooling chamber, which can be partially or completely filled with coolant to cool the extrudate as it passes through the chamber. Alternatively, instead of immersing the hot extrudate in coolant, the cooling chamber can have spray nozzles which spray the extrudate with the coolant to effect the cooling process. The cooling processes in the vacuum chamber, calibrators and the cooling chamber can be controlled by conventional electronic devices in a known manner which is described in more detail below. Other coolant mediums which have been used in cooling processes can be referred to collectively as refrigerants, including cryogens. Cryogens include liquid nitrogen, liquid carbon dioxide, liquid air and other refrigerants having normal boiling points substantially below minus 50xc2x0 F. (xe2x88x9246xc2x0 C.). Cryogens, due to their extremely low boiling point, naturally and virtually instantaneously expand into gaseous form when dispersed into the air. This results in a radical consumption of heat. The resilient temperature can be reduced to hundreds of degrees below zero (Fahrenheit) in a relatively short time.
Conventional methods of chilling extrudates can include feeding a continuous hot extrudate from the extruder through a vacuum chamber, or calibrators, and then to a cooling chamber which cools the hot extrudate to a desired temperature. Although the vacuum chamber and calibrators provide some initial cooling, the cooling is generally mainly provided in the cooling chamber. From the cooling chamber the cooled extrudate is fed to cutting blades which can cut the cooled extrudate into sections of the desired lengths. The temperature of the extrudate when cut by the cutting blades can be crucial to obtaining an acceptable product. If the temperature of the extrudate is either too hot or too cold when it is cut, the cut sections can be of unacceptable quality. For example, if the extrudate is too cold when cut, deformation or fracturing can occur. Conversely, if the extrudate is too hot when cut, the ends of the cut sections may stick together. In additional to problems with the cut parts, the extrudate may warp if the temperature is not controlled properly. Consequently, it can be vital to control the temperature of the extrudate to prevent warping and so that it is within a certain desired range of temperatures at the point where it is cut by the cutting blade in order to produce products of an acceptable quality. In order to obtain the proper temperature of the extrudate at the point of cutting, the conventional manner is based upon a manually performed trial-and-error process. For example, a certain temperature is estimated and the cooling chamber is brought to that temperature. Next, the quality of the cut is closely observed to determine whether the temperature of the extrudate is too hot or too cold. If the cutting process indicates that the temperature of the extrudate is too hot, the temperature in the cooling chamber is lowered, typically in a small increment to avoid overshooting the desired temperature. After the temperature adjustment has had an opportunity to take effect, the cutting process is again closely observed to determine whether the appropriate temperature has been achieved. If the cut quality again indicates that a temperature adjustment is needed, the process is repeated by adjusting the temperature in the cooling chamber and observing the cut quality. This procedure may be repeated until the cut quality indicates that the proper temperature has been achieved. In addition to the time required to arrive at the desired temperature, material is wasted with each cut that produces unacceptable parts until the proper temperature is finally achieved.
Accordingly, there is a need for an improved apparatus and method for bringing the extrudate to the proper temperature in a more efficient and less wasteful manner.
An apparatus and method for extruding and cutting an extrusion can be provided which more quickly and efficiently brings a hot extrudate to the temperature required to permit the extrudate to be properly cut. The apparatus can include an extruder for producing a continuous extrusion which can be fed through one or more of a vacuum chamber, calibrators, and a cooling chamber which brings the extrudate to the desired temperature. The extrudate can be fed to a blade for cutting the extrudate into desired lengths by various types of known conveyance mechanisms. The apparatus can include a temperature controller for controlling the temperature in the cooling chamber. The temperature controller can include a programmable processor for automatically regulating the temperature in the cooling chamber. According to a presently preferred embodiment, the apparatus can include one or more temperature sensors which can be positioned just prior to the cutting blade and/or just prior to the location where the extrudate is engaged by the conveyance mechanism in order to provide feedback on the temperature of the extrudate at one or both of those points. The temperature feedback can be provided to the temperature controller which can use the feedback to control the temperature in the cooling chamber so that the cut quality is enhanced and/or so that the extrusion is not deformed by the conveyance mechanism. The cooling system can utilize various coolants, including water and cryogens. Similarly to the conventional manner, the cut quality can be observed to determine when an acceptable temperature has been achieved. In contrast however, the temperature at the cooling chamber can be regulated directly from the actual temperature of the extrudate near the cutting blade, instead of simply gradually adjusting the temperature up and down based upon what the cut looks like, as in the trial-and-error method. This process can similarly be employed by observing whether the extrusion is being deformed by the conveyance mechanism. Also, once a proper temperature has been arrived at, that information can be stored in a memory portion of the processor in the temperature controller, which can then use that information as a reference point in the future each time the process is carried out using the same materials and cutting conditions. Thus, no observation of the cut quality need normally be done to start running the process the next time and the system can automatically adjust to changes in ambient temperatures. In order to ensure that the temperature of the extrudate is within a desired range of temperatures at the point at which the extrudate is cut by the cutting blade, the temperature controller can continuously monitor feedback from the temperature sensor near the cutting blade. Any necessary adjustments in the temperature can be automatically carried out by the temperature controller, thus eliminating much, if not all, of the manual adjustments previously required according to the prior art method.
Moreover, where calibrators are used additional temperature sensors can be utilized in conjunction with cooling circuits provided in the calibrators. The temperature feedback from such sensors can be provided to a temperature controller which can use such feedback to control the temperature of the coolant circulated through the aforementioned cooling circuits. Besides being used to generally control the cooling of the extrudate, similarly to as described in connection with the cooling chamber, this feedback information and temperature control can advantageously permit different surfaces of a multi-sided extrudate to be cooled at different rates.
Other details, objects, and advantages of the invention will become apparent from the following detailed description and the accompanying drawings figures of certain embodiments thereof.